Version 4.1.0.4 should be save compatible with earlier games, but in case of such a big update and so many complex scenarios in the game, guaranteeing a 100% lack of issues isn't really possible.

On the other hand, we'd like to make sure we leave people enough time to finish their PBEM games before updating to 4.1

Therefore, I recommend you do not update your copy if you still have a PBEM game running you want to finish.

Even more importantly though: make sure that you do the same way your opponent does: either neither of you updates, or both of you should.

Since TOAW has some really big scenarios that can take a while to play, we will not, for the time being, restrict access to the PBEM server for older versions, so you can finish the games under 4.0.1.23.

Please, for the same reasons, while you are still running 4.0.1.23, do not accept new challenges on the PBEM server, to avoid possible issues with playing against a 4.1 copy of the game.